This paper surveys in some detail the development of calculation methods for unsignalised intersections in West Germany. Firstly, it gives some comments and critical notes on the German guideline published in 1972 and the procedures adopted in the 1985 edition of the Highway Capacity Manual (USA). It describes the present state of the art, which comprises the calculation of capacities and queues with stationary and partially non-stationary streams by mathematical methods and by simulation models. Special attention is devoted to (1) critical gaps and move-up times; (2) recent formulae for capacity calculations; (3) delay and congestion; (4) impedance effects; (5) non- stationary traffic; (6) combination of disturbed traffic streams; (7) regression methods. In the future, two approaches are planned for evaluating the capacity of unsignalised intersections in West Germany: (1) a guideline providing a simple calculation method for a pencil and paper solution; (2) a simulation program facilitating a differentiated evaluation of specific situations. The new guideline only takes account of results for stationary traffic flows, and the appropriate consideration of impedance effects still needs considerable research. The differentiated consideration of non-stationarities and disturbed distributions of headways, and the evaluation of traffic flow near its limit of capacity, will be left to simulation calculations in practice.
Samenvatting